首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   169020篇
  免费   7300篇
  国内免费   937篇
  177257篇
  2022年   737篇
  2021年   1328篇
  2020年   969篇
  2019年   1062篇
  2018年   12896篇
  2017年   11572篇
  2016年   9251篇
  2015年   3623篇
  2014年   3316篇
  2013年   4216篇
  2012年   8674篇
  2011年   16816篇
  2010年   14472篇
  2009年   10532篇
  2008年   12680篇
  2007年   14237篇
  2006年   3210篇
  2005年   3731篇
  2004年   4265篇
  2003年   3846篇
  2002年   3185篇
  2001年   2378篇
  2000年   2216篇
  1999年   1893篇
  1998年   902篇
  1997年   886篇
  1996年   928篇
  1995年   759篇
  1994年   713篇
  1993年   732篇
  1992年   1512篇
  1991年   1342篇
  1990年   1283篇
  1989年   1280篇
  1988年   1179篇
  1987年   1111篇
  1986年   1006篇
  1985年   984篇
  1984年   965篇
  1983年   755篇
  1982年   605篇
  1981年   598篇
  1980年   547篇
  1979年   748篇
  1978年   621篇
  1977年   569篇
  1975年   527篇
  1974年   529篇
  1972年   615篇
  1971年   639篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
52.
To obtain insight into the role of lipids in the translocation of extramitochondrially synthesized proteins, we studied the ability of apocytochrome c to pass lipid bilayers. With polyacrylamide gel electrophoresis, the digestion of externally added apocytochrome c by trypsin, enclosed in lipid vesicles, was followed. The experiments demonstrate that apocytochrome c is able to pass a lipid barrier and this process shows both a lipid- and protein specificity. The most probable molecular mechanisms involved in this phenomenon are discussed.  相似文献   
53.
The complete amino acid sequence of histone H3 (135 residues) from the nematode Caenorhabditis elegans has been established. Microheterogeneity occurs at positions 96 and 100 of the chain. The sequences of the nematode H3 isoforms are very similar to the major chain of calf thymus H3 with which they show 4 substitutions in total. The major variant has cysteine in position 96. This is the first report of cysteine in this position in H3 from non-mammalian tissue. An exceptional methylation site has been detected at position 79. Various other sites of secondary modification are of a conservative nature.  相似文献   
54.
55.
The anti-DNP response to DNP-BGG is substantially suppressed in guinea pigs sensitized to DNCB. The degree of antibody suppression varies with the mode of skin sensitization and with the degree of conjugation of the challenging immunogen. Suppression of the anti-HSA response was also induced by the prior injection of CFA.  相似文献   
56.
57.
I.J.A. Urban  D. de Wied 《Life sciences》1982,31(22):2417-2424
The influence of systemically administered Des-Tyr1-α-endorphin (DTαE), Des-Tyr1-γ-endorphin (DTγE) and haloperidol on electroencephalographic (EEG) activity of the lateral septum complex (LSC) and the frontal cortex was studied in male rats. DTαE (2 μg) significantly increased whereas DTγE (10 μg) significantly decreased the amounts of activity in the 5 Hz band. In addition, DTαE promoted production of 15 - 20 Hz activity, while DTγE decreased the amount of 20 - 30 Hz activity. EEG activity exhibited a marked variability which persisted throughout the recording session following administration of the peptides. Haloperidol markedly decreased the proportion of 10 - 15 Hz activity. The alterations in EEG of the frontal cortex were similar to those in LSC but less pronounced. The differences in the time course and frequency bands affected suggest that the effects of peptides and haloperidol on EEG activity of LSC are not mediated by the same mechanisms.  相似文献   
58.
The purpose of this review is to provide a global perspective on Oncorhynchus salmonine introductions and put-and-take fisheries based on modern stocking programs, with special emphasis on freshwater ecosystems. We survey the global introductions of nine selected salmonines of the genus Oncorhynchus: golden trout, cutthroat trout, pink salmon, chum salmon, coho salmon, masu/cherry salmon, rainbow trout/steelhead, sockeye salmon/kokanee, and chinook salmon. The information is organized on a geographical basis by continent, and then by species and chronology. Two different objectives and associated definitions of ‘success’ for introductions are distinguished: (a) seed introduction: release of individuals with the purpose of creating a wild-reproducing, self-sustaining population; and (b) put-and-take introduction: release of individuals with the purpose of maintaining some level of wild population abundance, regardless of wild reproduction. We identify four major phenomena regarding global salmonine introductions: (1) general inadequacy of documentation regarding introductions; (2) a fundamental disconnect between management actions and ecological consequences of introductions; (3) the importance of global climate change on success of previous and future introductions; and (4) the significance of aquaculture as a key uncertainty in accidental introductions. We conclude this review with a recognition of the need to terminate ongoing stocking programs for introduced salmonines worldwide.  相似文献   
59.
60.
Summary In this paper the leaf-marking method as used for the study of the development and initial decomposition of floating leaves is described and the reliability of the various measurements is tested and/or discussed. Some general results obtained withNymphoides peltata (Gmel.) O. Kuntze in tanks and in the field are presented and crltically discussed. Autolysis followed by microbial decay was in all cases the most important factor by which leaves disintegrated. In the field plots animals were responsible for the disappearance of 22% of the total leaf area produced during a growth season. This is, however, the combined effect of consumption and damage succeeded by microbial decay. Real grazing can be estimated to be no more than 10% of the production of floating leaves. Fungi can have an important role in initial decomposition, especially after the flowering period, as is demonstrated forSeptoria villarsiae Desm. All damage types show temporal and, in the case of animals, also spatial distribution patterns.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号